If you could find a substance that repels oxygen
and nitrogen to a certain degree, could you make
that substance able to float? If you could stick
it to stuff, could we have floating cars,
amusement parks, and everything else you could
imagine?

Question Date: 2017-01-10

Answer 1:

This is a very interesting question. Basically
what you are saying is if we have some material
that can repel air, can we make it float?

My short answer is "possibly but not easy".
To make things float, you have to supply large
enough net external force that can fight the
gravity.

To largely reduce the gravity is not easy,
unless we move to another planet. So the other
possibility is to supply large net external force
that can fight the gravity. The first thing I want
to mention is the rocket. By combustion of the
fuel, the air is strongly propelled at the bottom
of the rocket, thus providing a strong enough
thrust against the gravity that can send the
rocket into space. If we have the material that
can repel air and apply them to the bottom, we can
provide a net force that is against the gravity.
But because the density of air is relatively
small, usually it is not strong enough to go
against the gravity and float in the air.

Answer 2:

No, it would not work. What would happen would be
like if you poured water onto oil (water and oil
repel each-other). Water is denser than oil, so it
will sink to the bottom and form a layer on the
bottom, while the oil sits on top. So unless
your oxygen-nitrogen-repelling substance were also
lighter than air, then it would fall to the
surface of the Earth just like anything else.
Gasses that are lighter than oxygen and nitrogen
like hydrogen, helium, and even water vapor do get
used to make balloons.